1. Field of the Invention
The present invention relates to a brake system of a vehicle. More particularly, it relates to an antiskid control device to prevent wheels of the vehicle from locking when the brake system is operated, so that drivability of the vehicle is maintained.
2. Description of the Related Art
In a brake system of a vehicle, a master cylinder connected to a brake pedal and a wheel cylinder provided in a brake mechanism of the wheel are connected to each other by a piping system. An antiskid control device as disclosed, for example, in Japanese Examined Patent Publications No. 49-28307 and 49-32494, has a construction in which, in the piping system, a valve for discharging a pressurized oil in the wheel cylinder and a pump for supplying a pressurized oil to the wheel cylinder are provided. Thus, when a locking condition of the wheel is sensed, the pressure in the oil in the wheel cylinder is quickly released. Subsequently, if the wheel returns to a braking condition, the pump supplies oil at a gradually increased pressure to the wheel cylinder.
During antiskid control, an oil pressure at least higher than the pressure held in a nonbraking condition must be maintained and a certain amount of oil must be supplied to the wheel cylinders. In a conventional antiskid control device, the pump is usually driven by an electric motor, therefore the size of the unit must be increased to ensure that a pressure and flow rate higher than a constant value can be maintained during antiskid control.